Xerographic charging apparatus



p 1966 J. J. CODICHINI ETAL 3,275,837

XEROGRAPHIC CHARGING APPARATUS 2 Sheets-Sheet 1 Filed Jan. 4, 1963 Fzi:H

/N|/EN7'O]/I?\f. JOSEPH J. CODICH ROLF W. EICHLER THOMAS F. HAYNE BYATTORNEY p 1966 J. J. CODICHINI ETAL 3,275,837

XEROGRAPHIC CHARGING APPARATUS Filed Jan. 4, 1963 2 Sheets-Sheet 2 I05-I25 v. T 60 CYCLE P F/G. Z

POSITIVE OUTPUT WAVEFORM POSITIVE CORONA THRESHOLD m APP IMATELY 4 o ooVOLTS flZjRO VOLTAGE LEyEL A 7 U V L \NEGATIVE CORONA THRESHOLD VAPPROXIMATELY 3700 VOLTS NEGATIVE OUTPUT WAVEFORM O1 +0 T TS-I SR-I AcINPUT INVENTORS.

TS-2 O JOSEPH J. CODICHINI ROLF w. EICHLER TS-3 G GN THOMAS F. HAYNE.

D. Y F/a'4 fl/g ATTORNEY United States Patent York Filed Jan. 4, 1963,Ser. No. 249,442 3 Claims. (Cl. 307-2) This invention relates in generalto xerography and, in particular, to an improved high voltage powersupply for use in a xerographic apparatus to provide effectiveunidirectional power to threshold type loads, such as corona dischargedevices.

More specifically, the invention relates to an electrical power supplycircuit for providing electrical power to threshold type loads, forexample, to supply electrical power to one or more corona dischargedevices of the type disclosed in Vyverberg Patent No. 2,836,725.

In the process of xerography, for example, as disclosed in eitherCarlson Patent No. 2,297,691, issued October 6, 1942, or in CarlsonPatent No. 2,357,809, issued September 12, 1944, a xerographic platecomprising a layer of photoconductive insulating material on aconductive backing is given a uniform electric charge over its surfaceand is then exposed to the subject matter to be reproduced, usually byconventional projection techniques. This exposure discharges the plateareas in accordance with the radiation intensity which reaches them andthereby creates an electrostatic latent image on or in the plate coatmg.

Development of the image is effected with developer material ordevelopers which comprise, in general, a mixture of a suitable pigmentedor dyed electroscopic powder, hereinafter referred to as toner, and agranular carrier material, which later functions to carry and togenerate triboelectric charges on the toner. More exactly, the functionof the granular material is to provide the mechanical control to thepowder, or to carry the powder to an image surface and, simultaneously,to provide almost complete homogeneity of charge polarity. In thedevelopment of the image, the toner powder is brought into contact withthe plate and is held thereon electrostatically in a patterncorresponding to the electrostatic latent image. Thereafter, thedeveloped xerographic image is usually transferred to a support ortransfer material to which it may be fixed by any suitable means. Aftertransfer, any toner powder remaining on the xerographic plate isremoved.

Since the disclosure of the basic concept of xerography by Carlson, avariety of xerographic reproducing devices are in use, on a commercialbasis, for general copying applications of the type normally encounteredin business, engineering or law offices. These machines are thereforeadapted to operate from a conventional commercial electricial outlet,that is, 110 volt alternating current outlet.

In general, the electrostatic charging of the xerographic plate inpreparation for the exposure step, the electrostatic charging of thesupport surface to effect transfer and the charging of the xerographicplate to aid in the removal of residual toner powder are accomplished bymeans of corona generating devices whereby electrostatic charge isapplied to the respective surface in each instance. For example, anelectrostatic charge on the order of 740 volts is applied to thexerographic plate surface in preparation for the exposure step. Toeffect this charge in preparation for the exposure step, there isimposed on the high voltage wire of the corona charging device, a directcurrent potential of from 7000 to 8000 volts, depending on the coronathreshold potential to the corona discharge device.

Patented Sept. 27, 1 966 Prior art power supply circuits, capable ofimposing a high voltage direct current potential to these coronadischarge devices from a low voltage alternating current source, havebeen costly to manufacture and to maintain.

It is, therefore, the principal object of this invention to improvepower supply circuits so that the circuit can be manufacturedeconomically.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is bad to the following detaileddescription of the invention to be read in connection with theaccompanying drawings, wherein: I

FIG. 1 is a schematic illustration of a xerographic reproducingapparatus having a number of corona discharge devices actuated by apower supply circuit in accordance with the invention;

FIG. 2 is a schematic wiring diagram of a preferred power supply circuitof the invention;

FIG. 3 is a curve showing the output voltage waveform from the powersupply circuit of FIG. 2; and,-

FIG. 4 is a schematic wiring diagram of another embodiment of a powersupply circuit.

General As shown, the xerographic apparatus comprises a xerographicplate including a photoconductive layer or lightreceiving surface on aconductive backing and formed in the shape of a drum, generallydesignated by numeral 20, which is journaled in a frame to rotate in thedirection indicated by the arrow to cause the drum surface sequentiallyto pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographicprocessing stations in the path of movement of the drum surface may bedescribed functionally, as follows:

A charging station, at which a uniform electrostatic charge is depositedon the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern of copy to bereproduced is projected onto the drum surface to dissipate the drumcharge in the exposed areas thereof and thereby form a latentelectrostatic image of the copy to be reproduced;

A developing station, at which a xerographic developing materialincluding toner particles having an electrostatic charge opposite tothat of the electrostatic latent image are cascaded over the drumsurface, whereby the toner particles adhere to the electrostatic latentimage to form a xerographic powder image in the configuration of thecopy to be reproduced;

A transfer station, at which the xerographic powder image iselectrostatically transferred from the drum surface to a transfermaterial or support surface; and,

A drum cleaning station, at which the drum surface is first charged andthen brushed or wiped to remove residual toner particles remainingthereon after image transfer, and at which the drum surface is exposed-to a relatively bright light source to effect substantially completedischarge of any residual electrostatic charge remaining thereon.

The charging station is preferably located as indicated by referencecharacter A in the schematic illustration of the apparatus. In general,the charging apparatus or corona charging device 21 includes a coronadischarge array of one or more discharge electrodes that extendtransversely across the drum surface and are energized from a highpotential source and are substantially enclosed within a shieldingmember.

Next subsequent thereto in the path of motion of the xerographic drum isan exposure station B. This exposure station may be one of a number oftypes of mechanisms or members such as desirably an optical scanning orprojection system, or the like, designed to project a line copy imageonto the surface of the photoconductive xerographic drum from a suitableoriginal.

The optical scanning or projection assembly consists of a copy board inthe shape of a drum, hereinafter referred to as copy drum 30, which isadapted to support copy to be reproduced and arranged to rotate in lightprojection relation to the moving light-receiving surface of thexerographic plate. Uniform lighting is provided by suitable lamps 31attached to a slotted light reflector 32 mounted adjacent to the copydrum.

A slotted light shield 33, adapted to protect the xerographic plate fromextraneous light, is positioned adjacent to the surface of thexerographic plate. A slot aperture in the light shield extendstransversely to the path of movement of the light-receiving surface ofthe xerographic drum 20 to permit reflected rays from the copy drum tobe directed against limited transverse areas of the lightreceivingsurface as it passes thereunder.

To enable the optical system to be enclosed within a relatively smallcabinet, a folded optical system including an object mirror 34, a lens35, and an image mirror 36, is used in the preferred embodiment of theapparatus.

A document fed through document guides 37 to the copy drum is removablysecured thereon by a suitable gripper mechanism for movement therewithin timed relation to the movement of the xerographic drum whereby aflowing image of the copy is projected onto the xerographic drum. Thecopy is held against the surface of the copy drum until gripped by meansof document retaining guides 38. Pressure guides 93 and document guard41 retain and guide the trailing edge of the document on the copy drum.After the copy is scanned, it is released from the copy drum to 'betransported out of the machine by the copy drum and document feed outrollers 42 through document feed out guide 43.

Adjacent to .the exposure station is a developing station C in whichthere is positioned a developer apparatus 50 including a developerhousing having a lower or sump portion for accumulating developermaterial 51. Mounted within the developer housing is a driven buckettypeconveyor 52 used to carry the developer material previously supplied tothe developer housing to the upper portion of the developer housing fromwhere the developer material is cascaded over a hopper chute 53 onto thedrum.

As the developer material cascades over the drum, toner particles of thedeveloper material adhere electrostatically to the previously formedelectrostatic latent image areas on the drum to form a visiblexerographic powder image; the remaining developer material falling offthe peripheral surface of the drum into the bottom of the developerhousing. Toner particles consumed during the developing operation toform the xerographic powder images are replenished by a toner dispenser54.

Positioned next adjacent to the developing station is the image transferstation D which includes suitable sheet feeding mechanism adapted tofeed sheets of paper successively to the xerographic drum incoordination with the presentation of the developed image on the drum atthe transfer station. The sheet feeding mechanism includes a sheetsource such as paper tray 60 for a plurality of sheets of a suitablesupport material, that is, sheets of paper or the like, separatorrollers 61 adapted to feed the top sheet of the stack of supportmaterial through a guide 67 .to a sheet conveyor mechanism 62 havingpaper grippers 63 thereon which carry the sheet support material intocontact with the rotating xerographic drum in coordination with theappearance of a developed image at the transfer station.

The transfer of the xerographic powder image from the drum surface tothe support material is effected by means of a corona transfer device 64that is located at or immediately after the point of contact between thesupport m'aterial and the rotating xerographic drum. The corona transferdevice 64- is substantially similar to the corona discharge device thatis employed at the charging station in that it also includes an array ofone or more corona discharge electrodes that are energized from asuitable high potential source and extend transversely across the drumsurface and are substantially enclosed with a shielding member. Inoperation, the electrostatic field created by the corona transfer deviceis effective to tack the transfer material electrostatically to the drumsurface and simultaneously with the tacking action, the electrostaticfield is effective to attract the toner particles comprising thexerographic powder image from the drum surface and cause them to adhereelectrostatically to the surface of the support material.

As the paper gripper mechanism continues to move forward in its closedcircuit, it will strip the support material from the xerographic drumand carry it to a fixing device, such as, for example, heat fuser 70,whereat the developed and transferred xerographic powder image on thesupport material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from theapparatus at a suitable point for collection externally of theapparatus. To accomplish this, there is provided a pair of deliveryrolls 65 and 66 by means of which the copy is delivered from the machineafter it is released by the gripper mechanism. Suitable cam means 68 and69 are provided at the receiving and delivery stations of the conveyormechanism, respectively, to actuate the paper grippers at these stationsto receive or discharge a sheet of support material.

The next and finatl station in the device is a drum cleaning station Ewhereat any powder remaining on the xerographic drum after the transferstep is removed and whereat the xerographic drum is flooded with lightto cause dissipation of any residual electrical charge remaining on thexerographic drum.

To aid in the removal of any residual powder remaining on thexerographic drum, there is provided a corona prec'leaning device 84 thatis substantially similar to the corona discharge device that is employedat charging station A. Removal of residual powder from the xerographicdrum is effected by means of a web cleaner device adapted tocontinuously feed a clean fibrous web material into wiping contact withthe xerographic drum, As shown, the web material 55 is taken from asupply roll 81 and transported around a cleaning or pressure roll 82,preferably made of rubber, onto a takeup or rewind roll 83.

Any residual electrical charge remaining on the xerographic drum isdissipated by light from a fluorescent lamp 85 mounted in a suitablebracket above the xerographic drum, a suitable starter and ballast beingprovided for energizing the fluorescent lamp.

Suitable drive means drive the xerographic drum, the copy drum, thesheet conveyor mechanism at predetermined speeds relative to each other,and to effect operation of the paper separator roll, and the web cleanermechanism, the latter being driven at a speed or speed whereby relativemovement between the xerographic drum and the web material is effected.Suitable drive means are also provided for effecting operation of theconveyor power supply circuit adapted to operate from a con- 1 ventionalcommercial electrical outlet, that is, a volt alternating currentoutlet. The power supply circuit consists of a stabilized transformerand modified voltage doubler circuits which provide at least twoseparate output voltages; one with positive voltage peaks above theeffective corona threshold and negative voltage peaks below the coronathreshold and the other with negative voltage peaks above the coronathreshold and positive voltage peaks below the corona threshold.

The stabilized transformer T, sometimes called a constant voltagetransformer, a static magnetic voltage stabilizer, or a ferrosonicvoltage stabilizer, is well known in the art and the specific details ofthe structure of the transformer will not be described in detail hereinsince it forms no part of the subject invention. Transformers of thistype are adequately described in the Radio Engineers Handbook publishedin 1943 by McGraw-Hill Book Co. Inc. However, it is noted that in thistype of transformer, the secondary portion of the magnetic core of thetransformer is saturated to provide the stabilizing action, the outputvoltage has a flat topped wave form which is a distinct advantage forthe particular circuit to be described in detail hereinafter. Anadditional useful feature of the stabilized transformer is that theloose magnetic coupling between the primary and the secondary thereofcauses the output current at short circuit to be sharply limited whichis of benefit as a safety feature both for personnel and equipment.

Referring now to FIG. 2, the power supply circuit consists of a highvoltage transformer, generally indicated by reference T, with a magneticshunt path MS between the primary winding TP and the secondary windingTS to provide loose magnetic coupling between the primary and thesecondary. The primary winding TP of the trans former is connected to asuitable source of electrical power, such as a 110 volt, 6O cyclealternating current outlet.

In the embodiment shown, the secondary winding TS is provided with tapsTS1, TS-2, TS-3, TS-4 and TS5. Tap TS is connected to ground which is areturn path for the high voltage output at terminals C, T and PC.Capacitor 0-3 is connected to taps TS3 and TS-S and operates inconjunction with the loose magnetic coupling of the transformer to causethe secondary portion of the transformer to magnetically saturate andthereby provide a stabilized transformer secondary voltage.

Tap TS-l of the transformer is connected directly to a capacitor C-llwith a parallel .bleeder resistor R-1. The bleeder resistor R1 is usedto discharge the capacitor C-l after input power has been removed fromthe power supply, so that no terminals remain hot on the power supplyafter the input power has been removed. The other terminal of capacitorC-l is connected to output terminals C and T and to one end of rectifierSR-l. The other end of rectifier SR-l is connected to tap TS3 of thesecondary winding of the transformer.

As shown, the output from capacitor C-l is connected to terminals C andT connected to corona charging device 21 and to the corona transferdevice 64, respectively both of these terminals being provided with apositive peak voltage above threshold voltage. With this arrangement,the capacitor C-l is charged on every other half cycle of secondaryvoltage from the transformer through the rectifier SR1 which blocksopposite half cycles of secondary voltage from discharging capacitorC-l. As a result of this charge on the capacitor 0-1, the output voltageas seen between the terminals C or T and ground is an AC voltage with aDC. bias voltage provided by the charge in capacitor C-ll.

As seen in FIG. 3, the output voltage to the terminals C and T issomewhat square in shape, a result of the output characteristics of thestabilizing transformer. This squared wave shape is more beneficial, asdescribed hereinafter, than a strictly pure sine wave as would normallycome from an ordinary high voltage transformer.

A similar circuit consists of the transformer secondary taps T S-2 andTS4, which with rectifier SR-2 connected in series with resistor R2,charges capacitor C-2 connected to the secondary tap TS-2 of thetransformer to impose an output potential on the output tap PC, which isa biased negative output voltage. The purpose of the resistor R-2 is tolimit current through rectifier SR2 under conditions when the output atthe terminal PC or when the corona precleaning device 84 connectedthereto is shorted to ground. Under normal operating conditions, thevoltage drop across resistor R-2 is almost insignificant.

The reason why a current limiting resistor is used in series withrectifier SR-2 and none is used in series with the rectifier SR-1 isthat under PC short circuit conditions, at larger direct current voltagecan appear across capacitor C-2, whereas under C or T short circuitconditions, capacitor Cl represents a noticeably smaller alternatingcurrentimpedance and the voltage across the tap TS-l and TS-3 will dropunder short circuit C or T conditions due to the loose coupling betweenprimary and secondary coils of the transformer. Also there is little, ifany, need to provide a bleeder resistor for capacitor C-2 because theenergy stored in capacitor 0-2 is noticeably lower than the maximumallowable energy storage for safety considerations. As shown in FIG. 3,the output wave shape through outlet PC is also a square wave.

The advantage of a square output voltage wave shape for use withcorotrons, used in a Xerographic reproducing machine, is that theeffective output voltage imposed upon the corona discharge device is afunction of the voltage above the threshold during any given cycle. In axerographic reproducing machine, the peak allowable voltage is limitedby the level at which arcing will first occur so that with the squaredwave shape, as shown, more power can be delivered at a given peakvoltage than could be utilized with a voltage output in the form of apure sine wave shape.

The operation of the circuit can best be explained by reference to FIGS.2 and 3. The stabilized transformer (T), with loose magnetic couplingbetween the primary and secondary, working in conjunction with capacitorC-3 provides a stabilized output voltage so that output voltages willchange less than five percent for changes of fifteen percent in inputvoltage. This, of course, is a necessary requirement for consistentoperation in that in the average commercial office, the power input to axerographic reproducing apparatus from a commercial electrical outletwill vary throughout the normal working day as a result of variations ofload imposed upon the electrical circuit within an ofiice building.

Operation of the modified voltage doubler portion of the circuit can beunderstood more readily if only the positive output section isconsidered initially "(consisting of the transformer secondary TS,rectifier SR-Z, capacitor C1 and resistor R-l). On half cycles of onepolarity, it can be seen that current will flow through the rectifierand charge the capacitor. Resistor R-l is used to bleed the charge fromthe capacitor so that voltage will not remain at the output terminalsfor any appreciable length of time after input power has been removed,but the resistance value is high enough so that the resistor hasnegligible affect on steady state circuit operation. When the secondaryvoltage reverses polarity, the rectifier will not conduct and thevoltage presented to the load will be the sum of the capacitor voltageplus the transformer secondary voltage. The resultant output voltageWave shape is that of the transformer secondary but with the positivepeaks increased in magnitude and the negative peaks decreased inmagnitude by the voltage across the capacitor.

It can be seen from the above that the flat topped wave shape from thetransformer is not distorted, but rather biased to provide higher peakvoltages of one polarity. This will provide a greater amount of energyfor the load than a sharply peaked wave form with the same peak value.The value of the flat topped wave form can be appreciated by noting thatthe effective power available for charging is approximately proportionalto the voltage above threshold squared, times incremental time and thatthe peak value is limited by the spark over voltage level.

Ordinarily, it is desirable to retain the short circuit current limitingcharacteristics of the transformer. However, the equivalent circuit ofthe shorted power supply is basically a series connection of thetransformer inductance and the capacitor. If the values of inductive andcapacitive reactance are nearly equal, the current limiting impedancewill be very low. Therefore, since the inductance of the transformer hasalready been determined by output voltage and stabilizationrequirements, the capacitor must be chosen to provide eitherpredominantly capacitive or inductive reactance in order to limit shortcircuit current. The choice will determine the shape of the loadregulation curve as follows:

(A) If inductive reactance is chosen, the output voltage will be nearlyconstant for load currents up to a given value determined by thetransformer design and then drop sharply to zero at a short circuitcurrent which may not be more than several hundred percent of rated loadcurrent. This will happen because the high reactance of the transformeris produced by a magnetic shunt with a series air gap. The magneticshunt is between the primary and secondary coils and tends to reduce thecoupling between the primary and secondary (or increases the internalreactance of the equivalent circuit) except that at nominal loading, theair gap presents a high reluctance (magnetic circuit impedance) to fluxbetween the coils and effectively provides close coupling between coils.As the secondary (load) current increases, the fiux density willincrease in the secondary portion of the magnetic core and thus causeprimary current and flux density to increase and the primary andsecondary fluxes are in opposition so that the series air gap in themagnetic shunt will not then present so high a reluctance in comparisonto the core proper (coupling primary and secondary) and flux will bediverted through the shunt, thus reducing coupling.

(B) I-f capacitive reactance is chosen, the output voltage will drop ina straight line from the open circuit value to zero at a short circuitcurrent value. Since the capacitor is used to limit short circuitcurrent, the transformer secondary voltage will not drop to zero atshort circuit because the capacitor will then be the transformer loadand an additional short circuit path will exist through the rectifierand a portion of the transformer secondary. Short circuit currentthrough the rectifier will be greater than that for conditions inparagraph (A) by the (inverse) ratio of transformer secondary turnsinvolved in each case. This follows from the fact that the transformerlimits secondary flux which is a function of current times transformerturns. Therefore, in order to limit secondary current, it is necessaryto add resistance in series with the rectifier (see resistor R-2 andrectifier SR4 in the negative output section of the circuit).

For the application in the xerographic apparatus shown, it is necessaryto draw a significant current for two positive corona devices so thecurrent limiting action of the transformer has been chosen for positiveoutputs as shown in the circuit diagram. The negative output does notrequire a large current and, in addition, it is desirable to maintain aconstant current for expected variations in barometric pressure,temperature, humidity, etc. The steep load regulation curve (nearly astraight line) obtained with capacitive reactance limiting current willprovide small variation in load current for'wide variation .of operatingconditions so the capacitor C2 is used to limit short circuit current.

As is well known, the corona threshold potential and the corona currentfrom an energized wire are functions of the wire diameter. In theembodiment of the Xerographic apparatus shown, the wire sizes of thecorona devices are such that the positive corona threshold potential ofthe corona charging device 21 and the negative corona transfer device 64is approximately 4000 volts and the corona threshold potential of thecorona precleaning device 84 is approximately 3700 volts. These valuesof corona threshold potential will vary with variations of temperatureand humidity.

In a preferred embodiment of the circuit of the invention, the values ofthe various elements of the circuit are chosen so that with a 115 voltinput to the primary of the stabilized transformer T, the outputvoltages are as follows:

Output Terminal C and/or T PC Positive Peak (Volts)slooo'iira'iiiiiiihi'fj 5,800

From the above table, it is apparent since the corona thresholdpotential of both the corona charging device 21 and the corona transferdevice 64 is approximately 4000, these devices will only emit positivecorona, since the maximum negative peak voltage of 3000 volts is belowthe threshold potential of these devices. In the same manner, the coronaprecleaning device 84 Will only emit negative corona since the maximumpositive peak potential of 3300 is less than the corona thresholdpotential of this device.

For other applications, for example, when arcing of a corona wire isdesired or can be tolerated, an ordinary transformer may be used in lieuof the stabilized transformer T, as shown in FIG. 4. In this embodiment,the power supply circuit is used to provide a positive peak voltageabove threshold voltage to only a single threshold type load, such ascorona discharging device 21.

As shown in FIG. 4, this power supply circuit consists of a high voltagetransformer, generally indicated T. The primary winding TP' of thistransformer is connected to a suitable source of electrical power, suchas a volt, 60 cycle alternating current outlet.

The secondary Winding TS is provided with three taps TS-l', TS-2' andTS3'. Tap TS3 is connected to a terminal G connected to ground which isa return path for the high voltage output at the terminal C or to thecorona charging device 21, which is connected thereto.

Tap TS-l' of the transformer is connected directly to a terminal ofcapacitor C-l. The other terminal of capacitor C-l is connected to theoutput terminal C and to one end of the rectifier SR1. The other end ofrectifier SR-l is connected to tap TS-3 of the secondary winding of thetransformer.

As shown, the output of capacitor C1 is connected to a terminal C which,in turn, is connected to a corona charging device 21 to provide thisdevice with a positive peak voltage above threshold voltage. With thisarrange ment, the capacitor C-1 is charged on every other half cycle ofsecondary voltage from the transformer through the rectifier SR-l whichblocks opposite half cycles of secondary voltage from dischargingcapacitor C1. As a result of this charge on the capacitor C-l, theoutput voltage, as seen between the corona charging device 21 andground, is an AC. voltage with a DC. bias voltage provided by the chargein capacitor C-l.

Although the output of this circuit has been shown as being connected toa corona charging device, this corona charging device was used merely asan example of a threshold type load, it being apparent that other typesof threshold type loads could be used in lieu of the corona chargingdevice shown. This high voltage power supply circuit can be used toprovide a biased A.C. voltage to an output terminal, the polarity ofbias being de-,

terminal with the rectifier polarity as shown in FIG. 4. In addition, itis realized that a conventional transformer having more taps could beused in the manner shown in FIG. 2 to provide both a positive thresholdpeak voltage and a negative threshold peak voltage to a pair ofthreshold type loads.

The following significant or novel features are obtained with the newpower supply circuitry:

(1) Corona charging (or similar phenomenon) equivalent to that obtainedwith filtered D.C. from a conventional voltage doubler (previouslyconsidered to be the most economical method) is obtained with:

(A) The rectifying element reverse voltage reduced by a factor ofapproximately four which results in a considerable cost reduction.

(B) The number of power supply components is reduced by one rectifyingelement and one capacitor per polarized (positive or negative) output.This allows a further cost reduction and causes the power supply to beinherently more reliable.

(C) The total efliciency of the corona emitting circuit is improved byallowing use of more efficient corona devices. That is, it is necessaryto use voltages somewhat above the corona threshold for stable coronacurrent and the circuit described provides lower current values(allowing a higher percentage of total corona current to be used forcharging, etc.) for a stable corona voltage level.

(D) The rectifying elements are not directly in series with the outputsand thus do not have to pass short circuit current.

As it is well known, the corona threshold potential and the coronacurrent from an energized wire are functions of the wire diameter.

While the invention has been described with reference to the circuitdisclosed herein, it is not confined to the details set forth sincemodifications thereof will be apparent to those skilled in the art. Forexample, the power circuit disclosed could be used for a single output,either positive or negative, by deletion of that portion of the circuitnot required. This application, therefore, is intended to cover suchmodifications or changes as may come within the purposes of theimprovements or the scope of the following claims.

What is claimed is:

1. A high voltage power supply circuit to provide a positive biased A.C.voltage between a first output terminal and a third output terminal anda negative biased DC. voltage between a second output terminal and saidthird output terminal, said power supply circuit including a stabilizedtransformer having primary input terminals adapted to be connected to asource of A.C. potential, and a secondary having multiple taps;

a first capacitor connected from a first tap of said secondary to saidfirst output terminal,

a first rectifier having its anode connected to a third tap of saidsecondary and its cathode connected between said first capacitor andsaid first output terminal,

a second capacitor connected between a second tap of said secondary andsaid second output terminal,

a second rectifier having its cathode connected to a fourth tap of saidsecondary and its anode connected between said second capacitor and saidsecond output terminal, and

said third output terminal being connected to a fifth tap of saidsecondary, whereby the positive peak voltage applied to said firstoutput terminal is greater than the negative peak voltage applied tosaid first outlet terminal and whereby said negative peak voltageapplied to said second output terminal is greater than the positivevoltage applied to said second output terminal.

2. A high voltage power supply circuit to provide a positive biased A.C.voltage between a first output terminal and a third output terminal anda negative biased DC. voltage between a second output terminal and saidthird output terminal, said power supply circuit including a stabilizedtransformer having primary input terminals adapted to be connected to asource of A.C. potential, and a secondary having multiple taps;

a first capacitor and a first resistor connected in parallel with eachother from a first tap of said secondary to said first output terminal,

a first rectifier having its cathode connected between said firstcapacitor and said first output terminal and its anode connected to athird tap of said secondary,

a second capacitor connected between a second tap of said secondary andsaid second output terminal,

a second rectifier and a second resistor connected in series, thecathode of said second rectifier being connected to a fourth tap of saidsecondary, and the anode of said second rectifier being connectedthrough said second resistor between said second capacitor and saidsecond output terminal, and

said third output terminal being connected to a fifth tap of saidsecondary whereby the positive peak voltage applied to said first outputterminal is greater than the negative peak voltage applied to said firstoutlet terminal and whereby said negative peak voltage applied to saidsecond output terminal is greater than the positive voltage applied tosaid second output terminal.

3. The apparatus of claim 2, including a third capaci tor having oneside connected between said third tap of said secondary and said firstrectifier and its other side connected between said fifth tap of saidsecondary and said third output terminal.

References Cited by the Examiner UNITED STATES PATENTS 2,375,458 5/1945Agnew et a1 307-2 2,965,044 12/1960 Johnson 307-2 3,005,110 10/1961 Elam321-20 X 3,067,376 12/1962 Kwast 321-20 X FOREIGN PATENTS 642,762 3/1937 Germany.

61,197 7/ 1926 Sweden.

MAX L. LEVY, Primary Examiner.

LLOYD MCCOLLUM, MILTON O. HIRSHFIELD,

Examiners.

L. R. CASSETT, T. J. MADDEN, Assistant Examiners.

1. A HIGH VOLTAGE POWER SUPPLY CIRCUIT TO PROVIDE A POSITIVE BIASED A.C.VOLTAGE BETWEEN A FIRST OUTPUT TERMINAL AND A THIRD OUTPUT TERMINAL ANDA NEGATIVE BIASED D.C. VOLTAGE BETWEEN A SECOND OUTPUT TERMINAL AND SAIDTHIRD OUTPUT TERMINAL, SAID POWER SUPPLY CIRCUIT INCLUDING A STABLIZEDTRANSFORMER HAVING PRIMARY INPUT TERMINALS ADAPTED TO BE CONNECTED TO ASOURCE OF A.C. POTENTIAL, AND A SECONDARY HAVING MULTIPLE TAPS; A FIRSTCAPACITOR CONNECTED FROM A FIRST TAP OF SAID SECONDARY TO SAID FIRSTOUTPUT TERMINAL, A FIRST RECTIFIER HAVING ITS ANODE CONNECTED TO A THIRDTAP OF SAID SECONDARY AND ITS CATHODE CONNECTED BETWEEN SAID FIRSTCAPACITOR AND SAID FIRST OUTPUT TERMINAL, A SECOND CAPACITOR CONNECTEDBETWEEN A SECOND TAP OF SAID SECONDARY AND SAID SECOND OUTPUT TERMINAL,A SECOND RECTIFIER HAVING ITS CATHODE CONNECTED TO A FOURTH TAP OF SAIDSECONDARY AND ITS ANODE CONNECTED BETWEEN SAID SECOND CAPACITOR AND SAIDSECOND OUTPUT TERMINAL, AND SAID THIRD OUTPUT TERMINAL BEING CONNECTEDTO A FIFTH TAP OF SAID SECONDARY, WHEREBY THE POSITIVE PEAK VOLTAGEAPPLIED TO SAID FIRST OUTPUT TERMINAL IS GREATER THAN THE NEGATIVE PEAKVOLTAGE APPLIED TO SAID FIRST OUTLET TERMINAL AND WHEREBY SAID NEGATIVEPEAK VOLTAGE APPLIED TO SAID SECOND TERMINAL IS GREATER THAN THEPOSITIVE VOLTAGE APPLIED TO SAID SECOND OUTPUT TERMINAL.